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					| Evolution and Diversity |  
					| Lecture 9 2/25/98
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					| |  | Last week, we began looking at some of the biologic principles necessary to understand the history of life. | 
 |  | On Monday we looked at a film that detailed the diversity of life and how it was produced. | 
 |  | Todays, lecture will expand on that theme, and look at the evolution of diversity in animals. | 
 |  | Evolution of animals resulted from increasingly complex cellular interactions and advances in body plans. | 
 |  | These advances opened up new opportunities for animals in by allowing them to exploit into new environments. | 
 |  | New opportunities allowed further evolution of new forms. | 
 | From Protista to Porifera | 
 |  | Protista are single-celled "animals" | 
 |  | Porifera are colonial organisms | 
 |  | cellular level of organization | 
 |  | Cnidarians and Ctenophores | 
 |  | tissue level of organization | 
 |  | a simple sack forms the gut | 
 |  | Cnidarians show two modes of existence | 
 | Planula to flatworms (playhelminthes) | 
 |  | Playhelminthes contain a third layer of tissue | 
 |  | development of a head end (cephalization) | 
 | Development of the coelom | 
 |  | provides support for the organism | 
 |  | provides method for circulation | 
 |  | Coelom formed independently in two groups | 
 |  | Coelom-like structures formed in other groups (pseudocoelomates) | 
 |  | Coelom allowed expansion into new environments and life styles | 
 
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